A. Field of the Invention
This invention relates to a piston configuration for a reciprocating piston, direct injected internal combustion engine.
B. Related Technology
Various combustion chamber configurations for direct injected, reciprocating piston internal combustion engines are described and utilized in the prior art. In particular, pistons including a central recess or bowl for receiving the major portion of each fuel and air charge of each combustion cycle and into which the fuel is injected by a fuel injector are commonly utilized in diesel cycle (compression-ignition) and Otto cycle (spark-ignited) engines.
It is well known that the exhaust stream of diesel cycle engines in particular may contain high levels of particulate matter (p.m.) (i.e., soot and soluble hydrocarbons) that are observable as dark smoke discharged from the engine exhaust, such smoke containing various solids or particulates as well as gaseous substances, all of which contribute to undesirable atmospheric pollution. Government regulatory bodies have enacted various laws and regulations reducing the permitted amount of smoke and particulate matter that may be contained in a diesel engine exhaust stream with the objective of improving the quality of atmospheric air, particularly in urban areas or other areas exposed to high concentrations of pollutants caused by engine exhaust emissions.
Reducing the discharge of p.m. from such engines has become a major objective of diesel engine manufacturers world wide and various attempts have been made to achieve more complete combustion of the relatively heavy, high cetane fuels typically combusted in diesel cycle engines. Much attention, for example, has been given to the manner in which the fuel is injected and atomized in the combustion chamber of the engine and other approaches to the problem of unburned hydrocarbons have been taken with various results.
A specific combustion chamber arrangement that has been found to reduce smoke and particulate emissions from diesel engines is described in U.S. Pat. Nos. 4,898,135 granted Feb. 6, 1990, and U.S. Pat. No. 5,322,042 granted Jun. 21, 1994, both of which are assigned to the assignee of the present invention. In accordance with the aforesaid patents, one or more small reaction chambers are located adjacent the piston recess and communicate with the recess through openings that may be configured as slots or discrete orifices. The orifices are configured to produce a lag between gaseous flow of fuel and air into the reaction chamber and the discharge of partially reacted fuel radicals and intermediate species from the reaction chamber into the piston recess area. This produces a delayed infusion or "seeding" of radicals (the term radicals is always intended to include intermediate species) into the piston recess to the extent that a supply of radicals is produced in the reaction chamber in a first combustion cycle and part of the radicals are discharged into the next succeeding pre-ignition fuel air mixture to promote desirable ignition characteristics in the mixture and more complete combustion of the fuel of the mixture.
In accordance with the prior art as described in the aforesaid patents, the various arrangements of orifices produced a high degree of interaction between the reaction chamber and the piston recess area each combustion cycle and further produced a reduction in smoke and particulate emissions discharged into the exhaust stream of the engine. However, in order to meet increasingly stringent emission standards for diesel engines, further improvements were needed to promote more complete combustion of the fuel injected into the engine combustion chamber.